Reagent test strips are widely used in the field of clinical chemistry. A test strip usually has one or more test areas, and each test area is capable of undergoing a color change in response to contact with a liquid specimen. The liquid specimen usually contains one or more constituents or properties of interest. The presence and concentrations of these constituents of interest in the specimen are determinable by an analysis of the color changes undergone by the test strip. Usually, this analysis involves a color comparison between the test area or test pad and a color standard or scale. In this way, reagent test strips assist physicians in diagnosing the existence of diseases and other health problems.
Color comparisons made with the naked eye can lead to imprecise measurement. For this reason, a reflectance spectroscope is commonly used to analyze samples of body fluid. A conventional spectrophotometer determines the color of a urine sample disposed on a white, non-reactive pad by illuminating the pad and taking a number of reflectance readings from the pad, each having a magnitude relating to a different wavelength of visible light. Today, strip reading instruments employ a variety of area array detection readheads utilizing CCD (charge-coupled device), CID (charge-injection device) or PMOS detection structures for detecting color changes to the test strips. The color of the urine on the pad may then be determined based upon the relative magnitudes of red, green and blue reflectance signals.
Conventional spectrophotometers may be used to perform a number of different urinalysis tests utilizing a reagent strip on which a number of different reagent pads are disposed. Each reagent pad is provided with a different reagent which causes a color change in response to the presence of a certain type of constituent in urine such as leukocytes (white blood cells) or red blood cells. Typical analytes of interest for urine include glucose, blood, bilirubin, urobilinogen, nitrite, protein, and ketone bodies. After adding color-developing reagents to urine, the foregoing analytes of interest have the following colors: glucose is bluish green; bilirubin, urobilinogen, nitrite, and ketone bodies are green; and blood and protein are red. The color developed in a particular analyte defines the characteristic discrete spectrum for absorption of light for that particular analyte. For example, the characteristic absorption spectrum for color-developed glucose falls within the upper end of the blue spectrum and the lower end of the green spectrum. Reagent strips may have ten different types of reagent pads.
For example, to detect on immunotest strips or chemistry test strips the presence of blood in a person's urine, conventional reflectance spectroscopes have been used to detect the presence of blood in a urine sample disposed on a reagent pad. Any blood present in the urine reacts with the reagent on the reagent pad, causing the reagent pad to change color to an extent which depends on the concentration of the blood. For example, in the presence of a relatively large concentration of blood, such a reagent pad may change in color from yellow to dark green.
A conventional reflectance spectroscope detects the concentration of the blood by illuminating the reagent pad and detecting, via a conventional reflectance detector, the amount of light received from the reagent pad, which is related to the color of the reagent pad. Based upon the magnitude of the reflectance signal generated by the reflectance detector, the spectroscope assigns the urine sample to one of a number of categories, e.g. a first category corresponding to no blood, a second category corresponding to a small blood concentration, a third category corresponding to a medium blood concentration, and a fourth category corresponding to a large blood concentration.
In one type of reflectance spectroscope an optical system in the form of a readhead is used in which a light bulb is disposed directly above the reagent pad to be tested and a reflectance detector is disposed at a 45 degree angle to the horizontal surface of the reagent pad. Light passes through a first vertical optical path from the illumination source to the reagent pad and through a second optical path, disposed 45 degrees with respect to the first optical path, from the reagent pad to the reflectance detector.
Other devices have been designed to illuminate a reagent pad. For example, U.S. Pat. No. 4,755,058 to Shaffer discloses a device for illuminating a surface and detecting the intensity of light emitted from the surface. The surface is directly illuminated by a plurality of light-emitting diodes disposed at an acute angle relative to the surface. U.S. Pat. No. 5,518,689 to Dosmann, et al. discloses a diffused light reflectance readhead in which one or more light-emitting diodes are used to illuminate a reagent pad and in which light from the reagent pad is detected by a light sensor.
Many reflectometer machines are small enough and inexpensive enough to be usable in physician offices and smaller laboratories, for example, and therefore are able to provide individual doctors, nurses and other caregivers with powerful medical diagnostic tools. For example, U.S. Pat. No. 5,654,803, which is assigned to the assignee of the present disclosure and is incorporated herein by reference in its entirety, discloses an optical inspection machine for determining non-hemolyzed levels of occult blood in urine using reflectance spectroscopy. The machine is provided with a light source for successively illuminating a plurality of different portions of a reagent pad on which a urine sample is disposed, and a detector array for detecting light received from the reagent pad and generating a plurality of reflectance signals in response to light received from a corresponding one of the different portions of the reagent pad. The machine is also provided with means for determining whether the magnitude of one of the reflectance signals is substantially different than the magnitude of another of the reflectance signals. Where the body-fluid sample is urine, this capability allows the machine to detect the presence of non-hemolyzed levels of occult blood in the urine sample.
U.S. Pat. No. 5,877,863, which is also assigned to the assignee of the present disclosure and is incorporated herein by reference in its entirety, shows an optical inspection machine for inspecting a liquid sample, such as urine, using reflectance spectroscopy. The machine includes a readhead for illuminating a target area substantially uniformly via only a single light-emitting diode and receiving light from the target area so that reagent tests may be performed. The readhead is provided with a housing, first and second light sources mounted in a fixed position relative to the housing, a light guide mounted to receive light from each of the light sources which conveys, when only one of the light sources is illuminated, substantially all of the light from the light source to illuminate a target area substantially uniformly, and a light detector coupled to receive light from the target area. Each of the first and second light sources is composed of only a single light-emitting diode for emitting substantially monochromatic light of a different wavelength.
Other optical readers are known that do not use reflectance, but rather capture an image of the test strips and convert the captured signal to RGB or to another format from which the color of the reagent pads on the test strip can be determined. U.S. Pat. No. 5,408,535, which is also assigned to the assignee of the present disclosure and is incorporated herein by reference in its entirety. These optical readers can also be used to read slides or other diagnostic tests.
As mentioned above, such optical inspection machines provide individual doctors, nurses and other caregivers with powerful medical diagnostic tools. Since space is limited, there is a need to make these devices even smaller. According to one aspect of the present disclosure, this can be accomplished by reducing the optical path between the detector and the reagent pad. Furthermore, a need exists to permit the device to read more than one reagent strip at a time or a combination of urine strips and reagent cartridges at the same time. The spectrometers of the prior art have not met these needs.